Abstract
In this paper, tapping torque is experimentally and theoretically investigated. In the conventional analyses, the specific cutting resistance K acting at every cutting edge in the chamfer of a tap is dealt as if it were constant, and the equation to calculate tapping torque is given as follows : Mr=∫rr0KrdA=K∫rr0rdA, where, Mr : tapping turque, r : distance of cutting edge from the axis, r0 : radius of atap hole, dA : infinitesimal strip of a cutting area. From this study, it is clarified that K varies with r as shown in the following relation : K=K (r) =K0ea (r-r0) , where, K0, a : const.
This leads to the following new general equation for calculating tapping torque. Mr=∫rr0 K (r) rdA. The results obtained are as follows. (1) In one investigation using S35C steel, specific cutting resistance K (r) changes from 270 kg/mm2 to 880 kg/mm2 depending upon r and in another using BsBM2 brass, from 104 kg/mm2 to 260 kg/mm2. (2) Function K (r) is experimentally obtained by conventional fluting with cutting-off tools which have the identical cutting edges as in the chamber of the tap used. (3) Our new equation gives the theoretical torque curves which coincide exactly with the curves obtained by experiments.
